Should You Pre-check File Access Permissions in .NET?

.NET File Access Checking: Best Practices to Avoid Redundant Operations

When working with files in .NET, it may seem like a good idea to pre-check file access permissions, but this is not a recommended practice for the following reasons:

Dynamic nature of file access permissions

File permissions may change at any time, so pre-checking is unreliable. Even if you successfully check access permissions, the permissions may have changed before you tried to open the file. Additionally, other factors such as file locking, network availability, and path resolution can affect the results.

Redundant and slower than exception handling

Pre-checking files is redundant because even with pre-checking, exception handling code is still needed to cope with changes in permissions or file existence status. While exception handling is slower than some operations, it is still much faster than disk I/O, which is called when checking file permissions or existence.

Increased code cost and potential bugs

Pre-checking files increases code maintenance overhead. Additionally, they can introduce subtle bugs if file access status changes between check and open attempts.

Recommended method

Rather than pre-checking file access permissions, simply try to open the file and handle any exceptions that arise. This approach minimizes code costs, improves performance, and reduces the risk of subtle bugs. By focusing on robust exception handling, you can effectively cover all situations where file access is denied, whether the cause is permissions, locking, or the file's existence.

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